Circulation changes on Antarctic Peninsula from ice cores

Circulation changes on Antarctic Peninsula from

ice cores

Liz ThomasLiz Thomas11, Gareth Marshall, Gareth Marshall11

Joe McConnellJoe McConnell22 & Paul Dennis & Paul Dennis33

1.1. British Antarctic SurveyBritish Antarctic Survey2.2. Desert Research InstituteDesert Research Institute3.3. University of East AngliaUniversity of East Anglia

BAS Core locations

• Beethoven– 1991 – 1948

• Berkner– 948 m (completed 2004)

• Dolmen Island– 1982- 1651

• Dyer Plateau– D1 1988-1820

– D2 1989-1506

• James Ross Island– 365 m (completed 2008)

• Gomez– 2006-1850

James Ross IslandFaraday

Rothera

Dolman IslandDyer Plateau (1&2)

Gomez Berkner Island

Beethoven

Drill site

• Medium depth ice core drilled

to a depth of 136 meters with

an electromechanical, 104 mm

diameter drill

• Encompasses the period

between 1855 – 2006 (150

years)

• Ground penetrating radar

(GPR) used to asses

accumulation variability

Gomez ice core (73.59°S, 70.36°W, 1400 m a.s.l)

Site selection

• Strong SAM signal from reanalysis data

• High accumulation site

– High resolution records

• Increased elevation (1992-2003), thought to

be due to greater snowfall

– satellite altimeter data

– [Davis et al., 2005; Wingham et al., 2006].

Correlation between SAM and precipitation from ECMWF 1980-2004

Methods

• Continuous Flow Analysis with Trace

Elements-Dual

• The annual accumulation record was

derived using two methods:

– winter-winter value determined from the

minima of hydrogen peroxide (H2O2)

– summer-summer value based on maxima in

non-sea salt sulphate (nssS)

• Estimated uncertainty in the dating is ±1

year from 1855 to 1875 and <<1 year from

1875 to 2006

Gomez Accumulation

record

• Annual thicknesses converted to

water equivalents

• corrected for thinning assuming a

linear strain rate

• Doubling of accumulation: the mean

for 1855-64 was 0.49 mweq y-1 while

that for 1997-2006 was 1.10 mweq y-1

• Most rapid increase in recent period,

following a slight reduction in the

1970s

Annual snowfall at the Gomez site (dashed) and decadal average (solid)

Elizabeth R. Thomas., G., J, Marshall., Joseph R. McConnell, (2008), A doubling in accumulation in the western Antarctic Peninsula since 1850, Geophysical Research Letters, 35

Atmospheric circulation

Two principal spatial patterns related to known modes of atmospheric circulation variability

1. SAM

– strong negative correlations over the Antarctic continent with ring of positive correlations to the north (exception of the south-east Pacific)

Correlation map of Gomez accumulation vs. 500 hPa geopotential height, 1958-2006

Atmospheric circulation

• Correlation, SAM and the Gomez accumulation record is 0.41

• 28% of the increase in snowfall (1957-2006) due to positive trend in the annual SAM

Correlation map of Gomez accumulation vs. 500 hPa geopotential height, 1958-2006

Relationship with ENSO

• No significant relationship over

the entire 1866-2005 period

• Some periods when significant

(<10% level) positive correlation

with the SOI: El Niño = less

accumulation

• But also periods when negative

correlations exist

Running 21-year correlations between Gomez accumulation and the Southern Oscillation Index

Marine signal

• Large marine input

– Average Na+ (1854- 2006) 39 ppb

• Increase in sea salts since 1950’s

• Changes in sea salt ratio’s

– increased continental input?

• Is changing atmospheric circulation

affecting the marine signal?

Back trajectories

• BADC (www.badc.ac.uk)

• Daily release over 5 days

• Location, height, temperature

• To help identify source of chemical and

isotope signal in ice core

• Combined with satellite data to identify

individual storm events

2 weeks of back trajectory data from Gomez site (Jan 2004)

Isotopes

• Isotope (18O) record

• Compared with 18 months surface

temp from AWS (r2 = 0.89)

• In combination with other chemistry

and a mean seasonal cycle of

precipitation, aim is to derive

seasonal time series

• Back-trajectory analysis to try to

understand intra-annual variability Isotope record from Gomez approx bi-weekly resolution

Conclusions

• The Gomez ice core reveals a doubling of accumulation over the past 150 years

– change is restricted to the central and southern Antarctic Peninsula

• The SAM is a major driver of accumulation variability in the region. – Gomez accumulation provides a good proxy of the SAM – next step to compare with 150 year SAM reconstructions

• No consistent ENSO signal in SW Peninsula accumulation (similar to West Antarctica)

• Gomez core will allow us to derive a temperature record in the southwestern peninsula since 1850 and several other proxy records at a sub-seasonal timescale

• Back trajectories used to identify source of ins in ice core– Help answer questions relating to sea ice effect on temperature